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I Want to take a compression test on my 8n what is the best way to do this 1. with the hood on or off? 2.engine warm or cold? 3. What should the numbers be? 4. Can it be run with the hood off if so is there a adapter to hook up the gas tank 4. S/N is n344713 thanks....Chris.....
 

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A compression test is usually done with the coil wire pulled and on one cylinder at a time. You remove a spark plug and insert the compression tester....turn the engine over approx ten times and record the reading. Repeat that on all cylinders and compare readings. Readings should be ( I think) around 125 - 135 PSI per cyl. Taking the test on a cold engine and then again on a hot one takes you to next level of interpreting the readings. Different readings tell you how well the valves are seating during operation. There are probably publications out on how to interpret compression readings.
 

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I got my compression tester at Harbor Freight and I can screw it in with the hood in place. If you take the hood off - just strap a small plastic gas can to the top of your battery and rig up a fuel line (I use ordinary aquarium plastic air hose).

First - do this on a warm engine. You are not trying to see engine conditions with it sitting there cold - you want to see how it is when you are USING it. Besides, it was DESIGNED for moving parts to expand when hot to the correct specs. No need to pull the coil wire - just don't turn the key on (the starter button will still work). Make sure to open your throttle all the way and ensure the choke is not on. If you want, take one reading, then add a few tablespoons of oil and retake the test. This will give you somewhat of an idea of the condition of your rings and cylinder walls or if low compression could be a valve seating problem depending on the difference in readings between the two. Also - make sure the battery is fully charged if you still have the stock 6V setup and take all the spark plugs out before testing to make it easier on the starter.

Make note of the first compression jump - the higher that needle jumps up on the first turn the better. Just crank it over until the needle stops raising - that is your compression reading. Brand new rebuilds see 120 psi or so - worn in will usually see about 100 - normal engines see around 90 - and worn out see 70 or lower. I have actually seen a nice running engine though that started up quickly with 60 psi - but it was dead on 60 psi on all cylinders. Ford specs say 90 is the minimum - personnaly I say that is normal.

More important than high compression is consistant psi readings. It is a far better engine that has 90 psi in all 4 cylinders than one that has 90/110/100/105. Also - be weary of reading that are much lower and in adjacent cylinders - such as 100/85/85/100 - could mean a head gasket failure.

Probably more than you wanted to know - but I actually have more info I could give.

Good luck,
Dan
 

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I agree with Dan.. on a warmed engine.. and do a dry test then wet test.

fuel off, ignition off, and throttle open max.

90 psi minum per ford. though i've seen alot of workers inthe 70 range that start and run good..

dry tests that come up on wet are usually rings.. low dry / wet numbers are generally valves..

soundguy
 

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What happens if the tractor can't start?
 

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Why dredge up an 8 year old thread? Start a new one.

If the tractor has fuel, air, compression and spark @ the right time it WILL run.
 

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